Existing communication networks such as 4G networks allow the locations of user equipment devices to be tracked. The locations can, for example, be tracked by a core network communicating with a device or with a base station to request the location of a device. In future networks it is planned that network infrastructures (radio access networks (RANs)) of multiple protocols (e.g. 3G, 4G, Wi-Fi) will cooperate to allow a device to communicate using any of those protocols. In a hybrid network of this type some the underlying network protocols may have different or limited support for location tracking. It is therefore not straightforward to track locations across multiple protocols in such a future network.
In existing mobile networks, communication devices or user equipment (UE) entities can move around without setting up an active connection to the network. This is advantageous in that it saves energy and radio resources. Existing mobile networks such as 4G networks can track the location of UEs when they are in that state. That state is commonly referred to as the IDLE state. One reason for this is to allow the network to estimate by which base station(s) or access point(s) the UE can be reached in case a need arises to signal it or send data to it.
In the current 4G system, the location of a UE that is in the IDLE state is tracked in the core network (CN) using the location registration (LR)/location update (LU) procedure. This may for example involve the TAU procedure defined in “3GPP TS 24.301 V14.0.1 Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3” and “3GPP TS 23.401 v14.0.1 GPRS enhancement for E-UTRAN access”. This may be termed a form of CN-level location tracking. Specifically, the LR/LU operation is performed by a NAS between a UE and a mobility management entity (MME). This procedure is illustrated in FIG. 1.
For each LU operation, the UE needs to establish a communication channel to the CN. This includes the RRC procedure to setup a radio bearer to carry the LU (e.g. by TAU) signaling from the UE to the eNB, and the S1AP procedure to carry LU signaling associated with the UE from the eNB to the MME. It should be noted that the setting up of radio bearers can consume more radio resources and UE energy than other radio signaling such as beacons.
In current 4G networks the TAU is triggered by CN-level tracking policies. This may, for example happen when a UE crosses the boundary of a tracking area (TA), or when a previous location update times out. At that point the tracking area ID (TAI) is broadcast by the RAN. The UE checks the received TAI against a TAI list it previously received from the MME. If the received TAI is not in its TAI list, it sends a TAU to the MME.
In some non-3GPP RANs or RATs, for instance Wi-Fi, LT tracking and TAs are not supported.
R2-164129: “UE mobility tracking in ‘active state’ and in ‘power saving’ state” proposes a general framework for CN/RAN collaboration on location tracking. In this proposal location tracking functionality is split into RAN location tracking and CN location tracking. A RAN anchor is defined to act as the mobility anchor of a UE in the data plane. The CN LT function is responsible for performing UE location tracking at the CN level, performing policy based location tracking management and tracking/inquiring of UE RAN anchor and RAN LT changes. Once the RAN anchor is known, the CN can deliver downlink traffic for the UE to that anchor point. Then the RAN can deliver downlink traffic from the RAN anchor to the UE. The RAN LT function is responsible for performing UE location tracking in the RAN level according to the policy set by the core network LT function and reporting changes of UE RAN anchor or changes of RAN LT to the CN LT function according the policy set by the CN LT function.
As indicated above, future systems are expected to support multiple RANs. In these systems different RANs are expected to support different systems for indicating and detecting locations. According to “3GPP TR 22.891 Study on New Services and Markets Technology Enablers”, the indication of a UE's location when it is being tracked may be the ID of the base station serving the UE, the IDs of a group of base stations any of which is serving the UE, the MAC address of a Wi-Fi access point (AP), etc. The location of the UE could be detected directly in the RAN using a downlink (DL) measurement report or using an uplink reference signal from the UE as described in “WO2015/192884”.
Another factor is that in future networks it is expected that a considerably increased number of UEs will be connected due to an increased diversity of device types such as wearables and sensors.
In a future system it would be preferred for location tracking to be enabled for all RANs and/or radio access technologies (RATs) that are supported by the system. Location tracking should preferably be supported across different RANs and RATs. In addition, it would be preferred for the role of UE (i.e. the amount of signaling from the UE and the amount of processing performed at the UE) in order to support location tracking to be reduced, even compared to the current 4G system. This would save power at the UEs. In addition, it would be preferred for the amount of signaling in the RAN and the core network (CN) in order to perform and support UE location tracking to be reduced compared to the current 4G system.
For various reasons, the current 4G mobile telecommunication system is not able to satisfy these needs. Some reasons for that are:    1. The mechanism for location tracking in the current 4G system only provides location tracking for the 4G access network. It does not support integration with other RATs for location tracking. Whilst RAN-level tracking has been discussed (see R2-164129: “UE mobility tracking in ‘active state’ and in ‘power saving’ state”) it has not been determined how such a function could be supported at the core network: for example, how the CN could make use of RAN-level location tracking; (i.e. get the location tracking results from the RAN), how the CN could influence RAN-level location tracking, or how location tracking at the RAN level and at the CN level can be aligned.    2. In current 4G networks the UE always needs to use the NAS procedure (i.e. the TAU procedure described in “3GPP TS 24.301 V14.0.1 Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3”) to report its location to the CN. This means the UE needs to set up a communication channel to the CN to report on its location. Doing so consumes energy at the UE and occupies radio resources.    3. Because location reporting is performed on a per-UE basis, the amount of control signaling needed to do location updating is broadly proportional to the number of UEs. In future networks it is envisaged that there may be device densities of up to 2500 UEs/km2. This would require a great amount of control signaling. Also, if there are many UEs moving in a similar pattern (e.g. connected vehicles) they could even overload the control plane by sending location update simultaneously.
There is a need for a way of performing location updates in a communications network which supports better integration of multiple RATs and/or allows the amount of signaling to be kept down.